cvl423 post midterm review

a layer of cohesion less particles (particles cement together to form rocks)

Bed definition

gravel (>2mm)
sand (.06mm to 2mm)
silt (.003mm and .06mm)

clay is commonly any particles less than silt
​

3 Common sizes of clastic rock particles

silts and clays

what two particles do geologists call mud?

particles sizes are gravel

rounded (conglomerate) vs angular (breccia)

conglomerate v breccia

carbonates (ie. limestone)
evaporates
cherts
coals

Chemical Sedimentary Rock classifications (4)

Diluted HCl (acid)

carbonate rocks react to \___

entirely silica, silica rich groundwater/deep silica rich marine environments

Cherts are hard, dense rocks composed of \_____ and form in \____

lakes dry up and have a good crystalline structure

Rock salt and rock gypsum

evaporates form when \_____, some examples are (2)

continental
shoreline
marine

3 major sedimentary environments

atmosphere

evaporates must be close to the \___

buried in swamps

coal comes from decomposed organic mater and must be found \____

marine

limestones are \____ deposits

(plant fossils)
BLACK
no
deep under the ocean

shales can come from terrestrial (given indicator) or but \___ shale with \___ fossils comes from \____

Red
Black

\____ colour usually indicates terrestrial while \____ usually indicates deep sea

a numeric date is the actual number of years that have passed since an event occurred;

relative dating means rocks are placed in their proper sequence of formation (and order, not an age)

Numeric vs Relative Dating

in an undeformed sequence of sedimentary rocks, each bed is older than the one above it and younger than the one below

developed by Nicolaus Steno

Law of Superposition (definition and creator)

all surface-depositied materials including lava and ash

what does the law of Superposition apply to

horizontal
flat

Principle of Original Horizontality (dev. Nicolaus Steno)
layers of sediment are generally deposited in a _ position; rocks having _ layer have not been disturbed

continuous
all

grade into

thin out

Principle of Lateral Continuity: sedimentary beds originate as _ layers in _ directions until they (_ into a different type of sediment) or (_ out at the edge of a deposition basin)

fragments of one rock unit that have been enclosed in another rock

inclusions are older than the rock around them

what are inclusions?

an unconformity is a break or Gap in the Rock record, caused by uplift, erosion, subsidence and new sedimentation

What is an unconformity? What causes unconformities?

1. angular
2. disconformity
3. nonconformity

what are the 3 types of unconformities?

tilted or folded-up rocks are overlain by younger, flat lying rocks (indicates period of deformation occurred during a pause in deposition)

angular unconformity (DUES)

a gap in the Rock record representing a period of erosion
- layers above and below disconformity are parallel
(more common than other unconformities)

disconformity (DUES-parallel)

separates older metamorphic or igneous rocks from younger sedimentary strata (different rock types altogether)

nonconformity (DUES-completely different)

rocks of the same age in different areas of the earth can be matched up

correlation of Rock layers (Geologic Time)

physical criteria
fossils

what are the two types of correlation of rock layers used in geologic dating?

1. position of Rock bed in a sequence of strata
2. composition of distinct minerals
SHORT

how do we correlate Rock layers by physical criteria? better for short 9r long distance correlation?

William Smith noted sedimentary strata in widely separated areas could be identified and correlated by their distinctive Fossil content

used with physical criteria to correlate GREAT DISTANCES (between continents)

how do we correlate Rock layers based on fossils? who created it, and is it good for short or long distances?

T

(T/F) any time interval can be recognized by its fossils

geographically wide spread but
limited to short span of geologic time (presence allows us to match rock to specific period)

what are index fossils? are they geographically widespread?

a group of fossils that can be used to date rocks more precisely than a single fossil

what is a fossil assemblage?

ie. presence of clamshell fossils indicate regione covered by a shallow sea (approximation of ancient shoreline)

ie. fossils of coral (which live in warm seas) indicate a warm environment when fossil was forming (indicate past water temperature)

what are environmental indicators for geologic dating?

alpha emission - nucleus emits 2p, 2n (helium atom)
beta emission - nucleus emits 1e, a neuron converts to a proton
electron capture - nucleus captures 1e, converts a p to an n

what are the 3 types of radioactive decay?

F, an element will have the game number of protons

(T/F) the number of protons between an element and it's isotopes will change

the time required for half of the radioactive nuclei in a sample to decay

what is half life

1:1

what is the parent: daughter ratio for 1 half life

T

(T/F) the percentage of radioactive atoms that decays during one half life is always the same

F

(T/F) the increase in daughter atoms is not equal to the decrease in patent atoms

ideal since potassium in found in many minerals

Why is Potassium-Argon decay relationship ideal for dating

1. closed system required 2. temperatures cannot be too high (daughter products may be lost)
3. only fresh unweathered rocks can be used

what are (3) restrictions for sources of error with radioactivity

force acting equally in all directions

confining pressure definition

force in one direction is stronger than others

differential stress definition

differential stress

what causes deformation? (hint: stress)

- non permanent change in volume/shape (returns to initial conditions)
- permanent change in volume/shape (does not return to initial conditions, doesn't fracture)
- fracture occurs (stresses exceed strength of chemical bonds)

Elastic v. Ductile v. Brittle deformation (Crustal Deformation)

point where rock behaviour changes from brittle to ductile due to temp and confining pressure (~10-15km deep)

Brittle-ductile transition point:

Temperature, Confining Pressure, Rock Type, Time

factors affecting deformation (Crustal Deformation)

melting
ductle
cool
brittle

(Temp affecting Crystal Deformation) at high temperatures rocks are closer to _ point; weaker and more _; in _ environments, rocks are _ and prone to fracture

less
harder

increased pressure in all directions makes rocks _ brittle and _ to break; temperature and pressure have complemnentary effects

slowly
quick

(Time affecting Crustal Deformation) stress applied _ can accomodate ductile deformation but _ application will cause fracture

crystalline (igneous) vs layered (sedimentary, metamorphic)

Strong v. Weak Rock Types (Deformation)

fracture and
folding

How do strong crystalline rocks fail? how do weak layered rocks fail?

faulting (displacement) and joints (no displacement)

what are the two types of fracture? what are their differences?

igneous
strong
brittle
fracturing

crystalline rocks such as \_____ rocks composed of minerals with \____ interal bonds tend to be \_____ and fail by \_____

sedimentary
metamorphic
foliation
ductile
folding

\_____ and \_____ rocks with zones of weakness (such as \_____) tend to be \_____ and fail by \_____

footwall vs hanging wall

vertical displacement along faults

polished striated surface due to crustal blocks sliding against one another

loosely coherent rock forming near earth's surface (composed of crushed rock fragments)

Define the fault scarp, slickensides and fault breccia

movement parallel to slope of the fault surface, dominant displacement is vertical

Normal (haning wall moves down relative to footwall, results from tension stress, extension), reverse (hanging wall moves up relative to footwall where DIP OF FAULT PLANE IS \>45deg, resul of COMPRESSION) and thrust (like reverse but hangingwall moves up the fault plane, result of COMPRESSION stress, dip of fault place is

dip-slip fault

movement parallel to fault surface, dominant displacement is horizontal

right lateral (opposing 'block' shifts to the right) and left lateral (opposing block shifts to the left)

strike slip fault

faults that exhibit both dip and strike slip faults (both vert displacement and horizontal displacement)

caused by shear and tensionORcompression stress

oblique slip faults

fractures along which blocks have not moved, result of tension, shear or compression stresses

geologic joints definition

NO

do joints have layer displacement?

Brittle

joints are the result of \____ behavior in rocks

parallel, perpendicular

rocks fracture in a plane \_____ (perp/parallel) to max principal stress and \_____ (perp/parallel) to min principal stress

Y

chemical weathering tends to be concentrated along joints, Y or N

Y

Do joints play an important role in the transport of liquids?

Y

Do valuable minerals deposit along joint systems?

rocks which are bent into a series of wave-like patterns (compression)

geologic Fold definition (result of \_____ stress)

F, they do!

folds don't occur along convergent plate boundaries (T/F)

the two sides of a fold

a line drawn along the crest of the fold

the plane symmetrically dividing the fold

the inclined angle with horizontal of the fold axis (complex folding)

Fold terminology (Limbs, Hinge Line, Axial Plane, Plunge)

anticline (crest) and syncline (trough)

2 types of folds

younger rocks, older rocks

weathering of anticline folds reveals \____ rock first then \_____

both equally

weathering of syncline reveals oldest/youngest rocks equally/first/last

symmetrical, asymmetrical, overturning

3 fold orientations

folds coupled with a fault

monocline definition

strike - intersection of hori plane with rock's inclined plane

dip - maximum angle of the inclined plane from horizontal

strike and dip method (definitions)

90 deg

Dip is always what degree to the strike

return
free
frictional

earthquakes occur when rocks \____ to their original, stress -\_____ shape after overcoming the \______ forces exhibiting elastic rebound

huge amounts of energy released during earthquakes, travel through Earth's interior

seismic wave definition

Harry Fielding Reid, early 1900s

elastic rebound was first explained by \_____

1 build up of stress
2 slippage
3 strain release

remember the ruler snapping analogy

stages of elastic rebound (3)

hypo: point when rock slippage occurs

epi: location on Earth's surface directly above hypo

hypocenter and epicenter

fracture where blocks HAVENT MOVED (no layer displacement)
results of TENSION or shear or compression

joints definiton

brittle
parallel
perp

joints are the result of \____ brehaviour of rocks; rocks fracture in a plane \___ to maximum principal stress and perpendicular to \___ principal stress

chemical weather tends to be concentrated along joints
highly jointed rocks area risk to construct near/on
affect mechanical properties of the rocks
are an important role in fluid transportation
valuable mineral deposits along joint systems

significance of joints

rocks bent into wave-like structures
result of COMPRESSION stress along convergent place boundaries

folds definition

anticline: up-warped arched rock layers
syncline: down warped trough rock layers

geological fold terminology

fore: earthquakes occuring days/years before the big earthquake (do not actually do much to predict upcoming earthquakes)

aftershock: lesser magnitude earthquakes that occur after a strong earthquake (aftershocks help determine the size and area of slippage)

foreshock v aftershock

convergent - compression forces, as one continent collides with another, slice the earth along numerous thrust faults

transform - horizontal displacement between two plates parallel to the fault line (strike slip)

convergent v transform plate boundaries

F, differential displacement - it can be slow and gradual (creep), intervals of small/medium earthquakes, or some sections might remain locked, building up energy for a major earthquake

in large faults, displacement occurs the same amount throughout (TF)

the base of the device moves but the mass doesn't until the base does

seismographs & seismometers

body, surface

two main types of seismic waves

body travel through Earth's interior

surface waves travel in the rock just below earth surface, only crust

body waves v surface seismic waves

false, body before surface

surface waves arrive at seismic station before body waves (TF)

primary waves are a push-pull compression expansion in the direction of wave travel

secondary waves shake the rock in a perpendicular direction to wave travel (up down)

what are primary and secondary body waves?

up and down
side to side
more

surface waves cause Earth's surface to move either () or () which is () damaging to man made structures

P, S, Surface

order the arrival of P, S and surface waves first to last

S waves have slightly greater amplitude the P waves, but surface waves have greater amplitude than S waves and retain them for much longer

greater
greater

the () the time interval between first P wave and first S wave, the () the distance

triangulation

use () to find direction of earthquake